The resistance to shocks and to vibrations are parameters which are indispensable for characterization of the mechanical resistance of materials, instruments and apparatuses of all kinds. When the object being tested is of small or medium dimensions, it is tested on appropriate "vibration and shock tables", but when the dimensions are considerable it is necessary to install appropriate sensors at one or more points of the apparatus. This takes place when it is also required to monitor continuously, during normal operation, the condition of vibrations of a given apparatus, for example in vehicles and in electrical and electromechanical machines. For this purpose, use is generally made of electromechanical transducers of various types, such as those of the piezoelectric, capacitive and electrodynamic type.
However, there are particular situations in which such conventional sensors are subject to certain limitations associated with the "hostility" of the working environment. For example in the case of electrical machines, precisely at the points at which it proves useful to perform monitoring, intense electromagnetic fields are present, which may falsify the recording of the vibration parameters or which at any rate may give rise to undesired interferences with the electrical signals or even cause problems concerning the electrical insulation, on account of particularly high voltages.